1. Field of the Invention
The present invention relates to a battery charging device, and more specifically, to a battery charging device, which controls a charger to charge a battery as the voltage of the battery changes.
2. Description of the Related Art
By the progress of electronic technology and widespread of electronic communication devices, portable electronic devices, such as notebook computer, PDA(Personal Digital Assistant) and digital cameras, etc., are commonly used. For easy to carry, these electronic devices are developed to become light, thin, short and small. Besides, lightweight and portable, easy to carry, and long time power supply are the requirements for users to choose which to buy. Because the power consumption of the portable electronic devices is pretty high, the battery needs to be charged so as to achieve a long time power supply. Recently, lithium-ion batteries are commonly used. Although light weight and large capacity, lithium-ion batteries do not have a memorizing characteristic. Lithium-ion batteries are continuously charged with a constant voltage.
Please refer to FIG. 4, showing a block diagram of a battery charging device of a conventional portable electronic device. The conventional charging device comprises a portable electronic device. The portable electronic device has a battery 30, a charging unit (Charge IC) 31, a programmable chip 32, and a charger 4. The charger 4 has an external alternating-current power source.
Please keep on referring to FIG. 4. The charging unit 31 is a switching direct-current to direct-current buck unit to supply charging current to the battery 30. However, the programmable chip 32 records data and conditions required for charging the battery 30. The data and conditions are all pre-set. For example, how much voltage and current are needed to charge, which conditions should be met then the battery 30 can be charged, and which power source should be cut off after the battery 30 is full-charged, etc.
When detecting the battery 30 is needed to charge, the programmable chip 32 will send signals to notify the charging unit 31 to charge the battery 30. After that, the programmable chip 32 notifies the charging unit 31 to switch off the charging power source to stop charging.
Although the conventional battery charging device can use the method of detection and determination to control charging of the battery 30, the conventional charging unit 31 cannot work independently, and therefore has to cooperate with the programmable chip 32 to operate such that the constitution components thereof are limited. This kind of assembly needs more components and thus does not have economic effects. Because the voltages between the initial and final stages of charging the battery 30 significantly differ, and the output voltage of the existing external charger is constant and unchangeable, the waste of circuit traces increases to cause instability of the devices and shorten the life.